There are, in present day use, numerous different types of windpower systems or wind turbines used to generate electrical power. These systems usually include a shaft-mounted turbine whose torque output is used to drive an electrical generator. When wind conditions are favorable, the electrical output from the generator is coupled into the electrical utilities' transmission lines. On the other hand when the wind speed is too low, the generator is isolated from those lines. In order to operate the generator at its optimum speed for maximum power output, the wind turbine must produce a selected relatively constant torque despite changes in wind speed. This is accomplished in most systems by sensing the rotational speed of the turbine. To maintain constant output power then, the pitch of the turbine blades is varied so that the blades intercept more or less of the moving air stream momentum thereby to regulate the torque output of the turbine and, as a result, its speed.
Prior windpower systems have employed pitch angle control mechanisms which are either more complex or less effective than that of this invention. Therefore, they are unduly costly to manufacture and repair, or are less effective in controlling the speed of the turbine. For example, some conventional turbines employ hydraulic pistons to change the blade pitch, with the fluid flow in the pistons being controlled by a speed-controlling governor. Examples of such arrangements are disclosed in U.S. Pat. No. 2,832,895 and on page 351 of Van Nostrand's Scientific Encyclopedia, Third Edition 1958. In another system, described in U.S. Pat. No. 2,583,369, the turbine hub is slidably mounted on its shaft. The turbine blades are terminated inside the hub by cams which slide in slots on that shaft. Also, springs bias the hub to a reference position on the shaft. As the wind exerts pressure on the blades, the hub slides in one direction or the other on its shaft so that the blades are cammed to the proper pitch.
Still another rather complex pitch control mechanism is disclosed in U.S. Pat. No. 2,360,792. That mechanism includes a hydraulic actuator and hydraulic compensated governor. The actuator's piston is connected to the turbine blades and the movement of the piston changes the blade pitch. In response to wind speed changes, the hydraulic governor delivers fluid under pressure to the actuator to cause the blades to assume their proper pitch.
Other prior windpower systems utilize various electrical components to control blade pitch, examples of same being described in U.S. Pat. Nos. 3,974,395; 4,095,120 and 4,160,170. However those arrangements require slip rings and other sliding electrical contact elements which are prone to failure due to surface corrosion, wear and contamination by dirt and moisture. In short, then, the prior systems are not as simple and trouble-free as they might be. Also some of them do not maintain adequate control over the turbine during unusual circumstances such as the occurrence of sudden strong winds which subject the components of the system to unusually high mechanical stress.
Also, in wind turbines such as this, it is essential that the pitch control mechanism be designed such that anticipated modes of failure drive the blades to their feather position at which they produce little or no torque so the turbine stops. For that purpose, prior apparatus rely on spring forces, complex battery-powered motor systems, or the self-feathering aerodynamic properties of the turbine itself. In some circumstances, such as where the blades or the pitch control mechanism is seized or ice-locked, these forces may be insufficient to feather the blades so that considerable damage to the turbine may result.